The Eagles on Thursday agreed to a six-year extension with Jason Kelce and a five-year extension with Riley Cooper. (USA Today Images)

The Eagles on Thursday locked up another offensive lineman for the long term, agreeing to an extension with center Jason Kelce, and, as expected, brought back receiver Riley Cooper.

Kelce, 26, signed a six-year extension worth $37.5 million, with $13 million guaranteed, according to a league source. The $6.25 million per year makes him among the top five highest-paid centers, a hefty haul for someone who has played just 34 games and hasn’t made a Pro Bowl.

Adam Caplan of ESPN.com first reported the extension.

Kelce is the first member of the 2011 draft class to have his contract extended. The new Collective Bargaining Agreement from 2011 precluded drafted players from signing extensions until after their third season.

“Jason is the epitome of the type of player we want around here, both on and off the field,” head coach Chip Kelly said in a statement. “He’s tough, extremely intelligent and is a leader by his actions and by his words. His athleticism is something that really sticks out when you watch him play. There aren’t many centers that can get down the field like he does.”

Cooper's contract is structured for five years, $25 million with $10 million guaranteed, but it’s really a four-year deal, according to a league source.

“Riley is one of the toughest and hardest-working guys in our locker room,” general manager Howie Roseman said. “We talk a lot about how players have to make the most of their opportunities, and he did just that last year. He used his size, strength and speed to make a lot of big plays for our team and I’m excited to watch him build upon his success.”

Kelce became the second offensive lineman this week to have his contract extended. The Eagles first rewarded left tackle Jason Peters with a new five-year deal on Wednesday.

All five starting offensive linemen from last year’s team that ranked fourth in scoring are under contract for 2014 as the Eagles prepare to defend their NFC East title in Kelly’s second season.

Kelce, entering his fourth season, came back from a major knee injury in 2012 to start all 16 games last season for an offensive line that paved the way for LeSean McCoy to lead the NFL in rushing and for an offense that set records for points scored and total yards.

Kelce missed most of the 2012 season after suffering the injuries in Week 2 against the Ravens. He underwent separate surgeries to repair a torn anterior cruciate ligament and medial collateral ligament in his right knee.

He came back this year, stepped back into his starting spot and helped anchor a record-setting Eagles offense that had undergone a schematic overhaul in Kelly’s first season and featured a starting quarterback switch from Mike Vick to Nick Foles.

The Eagles took Kelce in the sixth round of the 2011 draft, 191st overall out of Cincinnati. He was the team’s ninth draft pick in an 11-pick draft and is the only one from that class to receive an extension. He’s one of just three from that class who the team hasn’t yet released.

“You just don’t see many interior linemen with the athleticism that Jason Kelce possesses,” Roseman added. “It shows up on film many times where you just see him 10 or 15 yards down the field making blocks. His intelligence, work ethic and pride in his game are just off the charts. He’s the proverbial gym rat and is always at the NovaCare Complex working on his game. This was the first offseason we had to re-sign Jason and we jumped all over the opportunity.”